As many as one of every five worldwide terror threats picked up by U.S. government surveillance has been targeted on the United States, the Obama administration says. But officials are reluctant to say much more about the 50 plots they claim have been thwarted. (ASSOCIATED PRESS / Charles Dharapak, File)

WASHINGTON (AP) — Seeking to win over public trust, the Obama administration has been throwing around a lot of numbers as it tries to describe — in as much detail as possible without jeopardizing national security — the terror plots it says were thwarted by the government’s sweeping surveillance of U.S. communications.

There’s 50, 12, 10 and four. You also hear 20 and 90 in statements and official testimony, and even 702 and 215, though those aren’t for estimates of plots.

The numbers game is just part of the effort to convince skeptical Americans that the recently disclosed National Security Agency spy programs are vital in detecting and stopping extremist plots. But the approach has produced relatively limited, often vague information, and it has ended up confusing many in Congress as lawmakers grapple with how to assure people that their privacy rights are protected along with their security.

There are questions about effectiveness that still lack answers, “and we’ve gotten some answers that need further clarity,” House Intelligence Committee member Rep. Adam Schiff, D-Calif., said Thursday. He was referring to the so-called 215 program, which refers to the section of the anti-terror Patriot Act that authorizes the NSA to collect Americans’ phone records.

And, he added, “we also should ask in those cases where it was successful, how dated were the records.”

Another NSA program — known as 702 — authorizes the agency to sweep up Internet usage data from all over the world that goes through nine major U.S.-based providers.

Officials have used the rest of the numbers in Capitol Hill testimony over the past week as they have sought to allay Americans’ concerns that the programs violate their privacy.

Top officials told Congress that the programs have been key in thwarting at least 50 terror plots across 20 countries. And, they said, an estimated 10 to 12 of those plots were directed at the U.S. They publicly offered four examples among the 50-plus cases:

—An NSA-provided phone record led authorities to identify a terrorist financier in San Diego who was arrested in 2007.

—The NSA’s surveillance of Internet usage in 2009 revealed that a Chicago man, David Headley, was plotting to bomb a Danish newspaper that had published a cartoon of the prophet Muhammad, Deputy FBI Director Sean Joyce said. The FBI had been tipped off that Headley was involved in the deadly 2008 Mumbai terror attacks.

—Information from the NSA’s Internet usage surveillance of overseas operatives helped thwart a 2009 plot to blow up the New York City subway system. NSA Director General Keith Alexander said this information led investigators to Najibullah Zazi in Colorado. And the phone records collection gave investigators the connections between Zazi and his associates. Zazi ultimately pleaded guilty and provided information that helped send two of his friends to prison.

—A plot to blow up the New York Stock Exchange was thwarted in its early planning stages because the NSA was able identify an extremist in Yemen who was in touch with Khalid Ouazzani in Kansas City, Mo., Joyce said. This enabled investigators to identify co-conspirators and prevent the attack he said. Ouazzani pleaded guilty in May 2010 in federal court in Missouri to charges of conspiracy to provide material support to a terrorist organization, bank fraud and money laundering. Ouazzani was not charged with the alleged plot against the stock exchange.

The administration has yet to provide firm numbers of precisely how many plots have been stopped worldwide because of these programs — in part because intelligence officials are still trying to figure that out.

“The reason I’m not giving you a specific number is we want the rest of the community to actually beat those up and make sure that everything we have there is exactly right,” Alexander said Tuesday during a House intelligence committee hearing. “I’d give you the number 50-X, but if somebody says, ‘Well, not this one. Actually, what we’re finding out is there’s more. They said you missed these three or four.”’

Alexander said, “These programs are immensely valuable for protecting our nation and securing the security of our allies.” And the NSA’s authorization to sweep up Internet usage data has contributed to 90 percent of the information used to thwart at least 50 terror plots Alexander and his deputy told lawmakers.

On Wednesday, outgoing FBI Director Robert Mueller told the Senate Judiciary Committee that there are 10 to 12 cases in which the phone records surveillance program, authorized in the Patriot Act, contributed to breaking up terror plots.

He said that “of those, domestically, I think there will be anywhere from 10 or 12 where 215 was important in some way, shape or form.”

But later in the same hearing, Mueller said he’s not actually sure if it was the phone records authorization that helped thwart terror attacks in the 10 to 12 cases.

“I’m not sure whether all of them are 215. They’re a combination or the other,” Mueller said, referring to the phone records program and Internet usage programs.

FBI spokesman Paul Bresson referred requests for clarification to the NSA and National Counterterrorism Center. He said Mueller “was obviously unclear on the breakdown” since the FBI is not compiling the list of cases.

The confusion has, predictably, given rise to demands for more transparency by the intelligence agencies.

A growing number of Democratic and Republican lawmakers are pushing plans to open secret court orders authorizing the surveillance. Schiff, who filed House legislation on Thursday to match a similar Senate proposal, said it aimed at “allowing Americans to know how the court has interpreted the legal authorities” to ensure they are not being overly or improperly intrusive.

Additionally, a group of mostly Democratic senators are seeking to amend the Patriot Act to require the government to cite specific suspected links to terrorism or espionage before asking the secretive Foreign Intelligence Surveillance Court to approve the collection of Americans’ phone records.

But the legislation isn’t likely to be approved quickly, and confusion continues to hang over Congress and its constituents.

Noting frustration, Republican House Intelligence Committee Chairman Mike Rogers said trying to balance support for classified intelligence programs against a transparent democracy is always a challenge. But all concerned agree the current situation has fueled public skepticism.

“The public trusts their government to protect the country from another 9/11-type attack,” Rogers said this week, “but that trust can start to wane when they are faced with inaccuracies, half-truths and outright lies about the way the intelligence programs are being run.”